The invention relates to an injection casting apparatus for the manufacture of multiple part shoe soles, preferably double layer shoe soles of polyurethane, in a mold consisting of a side mold, an upper mold (last with shoe shaft) and bottom stamps to form at least a first and second hollow mold chamber, the mold being closed by one of two alternating bottom stamps.
To manufacture shoe soles by injection casting and simultaneously mold to a shoe shaft, either the intermediate sole facing the shoe shaft can be produced first and then be connected with the shoe shaft, whereafter the lower sole is manufactured and connected with the intermediate sole, or the sole layers can be formed in the reverse order. The latter method is commonly practiced in working with polyurethane.
The use of a plurality, particularly two bottom stamps for alternating closure of the hollow mold chambers on the side facing the sole is necessary for a number of reasons, particularly for the manufacture of soles with differently formulated layers. German OS No. 1,704,234 describes an injection casting apparatus in which an indexable turntable is provided with a plurality of multiple-element injection casting molds. In this apparatus two bottom stamps are alternately brought down into use from a position above the mold. The bottom stamps, in turn, are arranged on support arms disposed at a right angle to each other and which meet at a common rotating bearing lying outside the region of the mold. A drive mechanism is arranged alongside the mold, which can be raised and lowered and is also capable of rotating the support arms in such a manner that one or the other of the bottom stamps closes the mold or both bottom stamps are out of engagement therewith.
The bottom stamps in this known device are attached to the support arms in the lonitudinal direction thereof. In the closed position of the mold, however, this results in a static, unfavorable force transfer. The stroke and rotation apparatus is displaced relative to the bottom stamp currently in the operating position. This has the result that the closing forces transferred to the bottom stamps produce a significant additional torque. Furthermore, this apparatus is awkward to handle, because the rotation and stroke apparatus is disposed in the interior region of the rotatable table and the bottom stamp not in use is directed towards the center of the rotatable table.